If you're also having issues with the Clean Hands achievement, then I advise you to take a look at this: http://www.gamesas.com/topic/1417140-could-the-developers-give-us-exact-ghost-clean-hands-requirements-please/page__view__findpost__p__21663154

Don't forget you should also try and avoid sleep darting or choking Granny Rags on mission 7.

Yep. I'm also pretty frustrated. I've read somewhere on a popular gaming blog (PC gamer, was it?) that killing dogs shouldn't count, so I've killed a dog anyways not thinking it will go against getting the Clean Hands achievement. This has really left a bitter taste when I finished the game without seeing the achievement pop-up as I thought it would, but frankly, I think Arkane Studios should have made it so that killing dogs WILL affect the 'no one killed' checkmark in the end mission screen.

*le sigh*

Oh well, the game is still extremely enjoyable anyways with a lot of replayability so I'm sure that doing a second playthrough of the game just for the achievement will still be fun

Have fun assassinating!